The other things you changed in that commit was about NOT NULL for fields that are part of primary keys or unique keys.
pm_end_of_commitment_d is part of a unique key, but I see no reason why it should not be allowed to be NULL.
In general databases do not allow null values in primary keys, but for unique keys null fields are allowed.
The question then is if it makes sense to use a field which can contains nulls but only once per key.
If the column like this EoC Date can have any value and does not really make a distinction, then why use is at all as part of the unique key?
If part of a unique key, one could always choose to use a slightly different end date using nulls or dates nearby. Same for the start date.
It might be more useful to check for overlapping periods with other records.
